West Florida Shelf

A zone of deep-water reefs is thought to extend from the mid and outer shelf south of Mississippi and Alabama to at least the northwestern Florida shelf off Panama City, Florida (Figure 1). The reefs off Mississippi and Alabama are found in water depths of 60 to 120 m (Ludwick and Walton, 1957; Gardner et al., 2001) and were the focus of a multibeam echosounder (MBES) mapping survey by the U.S. Geological Survey (USGS) in 2000 (Gardner et al., 2000, Gardner et al., 2001). If this deep-water-reef trend does exist along the northwestern Florida shelf, then it is critical to determine the accurate geomorphology and reef type that occur because of their importance as benthic habitats for fisheries.

Figure 1. Location map showing northwest Florida shelf area mapped in 2001 (red rectangles, right side) and area mapped in 2000 on Mississippi-Alabama shelf and slope (green rectangle, left side).

In September and October of 2001, the USGS mapped the region between the 50 to 150-m isobaths south from the eastern edge of De Soto Canyon as far as Steamboat Lumps using a state-of-the-art multibeam mapping system (MBES)(red polygons labeled 2001 on Figure 1). The cruise used a Kongsberg Simrad EM1002 MBES, the latest generation of high-resolution mapping systems. The EM1002 produces both geodetically accurate georeferenced bathymetry and coregistered, calibrated, acoustic backscatter. Acoustic backscatter is the intensity of an acoustic pulse that is backscattered off the seafloor back to the transducer. The signal can give an indication of the type of material exposed on the ocean floor (i.e. rock vs. mud). These data should prove extremely useful in relating dominant species groups (which display highly specific biotope affinities) to the geomorphology (e.g., reef flattop, forereef crest, reef wall, reef base, circum-reef talus zone, circum-reef, high-reflectivity sediment apron, etc.).